FIG. 2 shows a prior art semiconductor laser device having a bent active layer. In FIG. 2, reference numeral 1 designates a p type GaAs substrate. A.sub.p type AlGaAs buffer layer 2 is disposed on p type GaAs substate 1. An N type GaAs blocking layer 3 is disposed on p type AlGaAs buffer layer 2. A.sub.p type Al.sub.x Ga.sub.1-x As lower cladding layer 4 is disposed on n type GaAs blocking layer 3 and p type buffer layer 2. An undoped Al.sub.y Ga.sub.1-y As active layer 5 is disposed on lower cladding layer 4. An N type Al.sub.x' Ga.sub.1-x' As upper cladding layer 6 is disposed on active layer 5. An N type GaAs contact layer 7 is disposed on upper cladding layer 6. Reference numeral 8 designates effective current flow and reference numeral 9 designates noneffective current flow. Herein, x and x' are larger than y.
The device will operates as follows.
The current injected from the p type substrate 1 flows through the p type AlGaAs buffer layer 2 and further through the p type Al.sub.x Ga.sub.1-x As lower cladding layer 4, the updoped Al.sub.y Ga.sub.1-y As active layer 5, the n type Al.sub.x'Ga.sub.1-x' As upper cladding layer 6, and n type GaAs contact layer 7. Herein, current is not injected except at a bent portion of the undoped Al.sub.y Ga.sub.1-y As active layer 5 because n type GaAs current blocking layers 3 are located between the p type AlGaAs buffer layer 2 and the p type Al.sub.x Ga.sub.1-x As lower cladding layer 4. As a result, an effective current 8 is injected into the neighborhood of the bent portion of undoped Al.sub.y Ga.sub.1-y As active layer 5, producing laser oscillation.
In the prior art semiconductor laser device having a bent active layer, a portion of the current injected from the p type GaAs substrate 1 is not injected into the bent portion of undoped Al.sub.y Ga.sub.1-y As active layer 5 but is injected into the flat portion at the both sides of the bent portion as noneffective current 9, increasing the threshold current.